The present invention is directed to ball screw and nut linear actuators and, more particularly, to those which are motor housing contained.
Applicant is aware of Vickers U.S. Pat. No. 2,444,886, wherein a gear driven shaft is operated by the armature of the motor and revolves a nut in an extension of the motor housing which is trapped so that it cannot be moved axially. A screw shaft of limited extensibility operates in conjunction with the nut. In this patent, the exciting field is fixed to the interior of the motor housing and the armature is radially inward of the field and operates the gearing mechanism. The structure disclosed in the Vickers patent is not compact and does not provide a screw which is unlimited by the other mechanism in terms of its permissible axial travel.
The present invention provides a linear actuator with a ball screw carrying a nut driven by an electrically energized motor which has an enclosing motor housing with both front and rear walls having aligned openings for axially passing the extensible ball screw. The helical grooves and lands formed in the nut and screw provide a helical ball raceway or raceways in which load bearing balls circulate in the usual manner. The electric motor integrated with the housing includes an inner stator assembly and an outer rotor assembly, and a partially enclosing can member integrated with the rotor assembly to rotate therewith. The rotating can has a radial wall with a driving connection to the nut. Two embodiments of the invention are illustrated in which the rotating can radial wall is attached to an end portion of the nut. In one case, the nut is concentrically located with respect to the stator assembly and the rotor assembly and, in the other, the nut is in line with the stator winding assembly.
One of the prime objects of the present invention is to provide a compact linear actuator of the type mentioned wherein the screw axial travel is limited only by the length of the screw.
A further object of the invention is to provide a linear actuator which is well adapted to use in a wide variety of applications, particularly where space requirements dictate that the linear actuator be compact and fit into restricted spaces.
Still another object of the invention is to provide a linear actuator which, in one embodiment, is well suited to accommodating side loads as well as axial loads.
A still further object of the invention is to design a linear actuator of relatively simple character which is economical to manufacture and market, and yet is durable in use and requires only a modicum of maintenance attention.
Other objects and advantages of the invention will become apparent with reference to the accompanying drawings and the accompanying descriptive matter.